Our research is devoted to the study of a fundamental membrane function of mammalian cells, namely the transport of macromolecules at the cell surface. This transport can be receptor-mediated or can occur in the absence of specific membrane receptors, in which case it is generally much less efficient. While our research encompasses both types of transport, our leading current interest is in procedures that will enhance the latter, i.e. that will facilitate the cellular uptake of maromolecules that are ordinarily only poorly transported. We have devised a procedure that dramatically increases the cellular uptake of such molecules (e.g. human serum albumin (HSA), horseradishperoxidase (HRP) into cultured established lines of fibroblasts, sarcomas and carcinomas. The procedure consists of conjugating to the protein a fragment of poly(lysine). When poly(lys) of 6700 MW is conjugated to HRP at a ratio of approximately 1:1, the cellular uptake of active enzyme is increased by a factor of 400. (PNAS 75, 1872-76, 1978). This striking finding has raised a number of fundamental questions which have formed the basis of the current year's research and which will set goal for the coming year. It was shown in particular that poly(L-lysine) is avidly taken up by cells and that it can serve as carrier not only for proteins but for drugs (PNAS 75, 3867-70, 1978).